We propose to establish a national facility at the Marine Biological Laboratory (MBL) containing advanced instrumentation based upon the ultrasensitive vibrating probe. This will enable various members of the biomedical community to efficiently map and measure the electrical fields around various living systems; and thus determine the pattern and (in part) the nature of the ionic currents which traverse these systems. The first installation will contain two nutating probe systems together with associated video and computer systems to efficiently reduce, display, and record the fields which are measured. Nutating probes provide simultaneous measurements of two components of the field at any point and should allow the effective exploration of the steady currents which traverse the acqueous media around minute cellular processes such as neurites as well as larger cells and tissues such as eggs and muscles. In due course we propose to develop further versions of the vibrating probe including an aerial one to measure fields near aerial systems (such as certain insect eggs, fungi, mammalian skin, etc.), and a three dimensional one. We plan to carry out various collaborative research projects, particularly ones on the role of endogenous currents in establishing pattern in certain marine eggs and in polarizing mammalian blastomeres, and the role of endogenous tip currents in controlling nerve growth. We expect to serve the needs of a very wide variety of biomedical users including persons interested in endogenous currents through muscle, nerve and blood cells, through various eggs and embryos, through growing plant cells, various functioning epithelia, regenerating limbs and nerve stumps and so forth. We likewise plan to provide appropriate training in the use of the vibrating probe.